SAN FRANCISCO (KGO) -- There were some unsettling moments for passengers on board a United Airlines flight from San Francisco to Tokyo when the plane was forced to return to SFO after experiencing an engine problem during take-off.

Dozens of passengers aboard a United flight to Japan are just getting ready to board another aircraft after their Boeing 747 experienced a mid-air maintenance issue.

United Flight 837 landed safely at SFO after the mid-air emergency.

Officials said one of the four engines was not working. Witnesses say they saw flames shooting from it shortly after take-off around 11:30 a.m.

Residents in nearby San Bruno heard loud booms. "I was upstairs and heard a loud boom several times more than once," San Bruno resident Mark Lawrence said.

"I didn't know what it was and then looked up and realized it was an airplane," San Bruno resident Juan Vega said.

The plane carrying 202 passengers and 15 crew members was heading to Tokyo when the mid-air emergency occurred.

Flight Tracker indicates it circled off the coast of Santa Cruz for some time.

Devin Durant, a passenger on the plane and photographer with AirlineGeeks, shared video of the 747 dumping fuel as it prepared to land.

An ABC7 News viewer and San Bruno resident says it also dumped a chunk of ice with toilet paper presumably from the lavatory. "The landing came more than three hours later," San Bruno resident Angelo Cruces said.

United officials didn't provide a comment, but an agent says the passengers were being re-booked onto another flight scheduled to leave at 4:30 p.m.